1. Field of the Invention
The present invention relates to a QoS routing technology for controlling communication quality of a network, and, more particularly, to a QoS routing technology for a logical network which can select an appropriate path from a plurality of candidate paths such as an overlay network and MPLS (Multi Protocol Label Switching) network.
2. Description of the Related Art
A QoS routing technology realizes a path selection and a path control based on a state of a network to optimize the rate of usage of a network resource and to improve communication quality. For example, Japanese Patent Application Laid-Open Publication No. 2006-109454 and Japanese National-Publication-of-Translated-Version No. 2003-502941 disclose technologies relating to the QoS routing.
Japanese Patent Application Laid-Open Publication No. 2006-109454 discloses a routing method in an overlay network. In the routing method, the cost of a default path (path without overlay node) from a source node to a destination node and the cost of alternate paths other than the default path are measured. The cost referred to here is a value calculated based on communication quality parameters such as a delay of a path, an available bandwidth, and the like to evaluate the path. The method of the publication improves network performance as to a delay, a throughput, and the like by selecting an optimum path based on a result of comparison of two types of costs.
Japanese National-Publication-of-Translated-Version No. 2003-502941 discloses a method of selecting a path in an MPLS network. In the method, the link costs of respective links in a network are changed based on a control strategic parameter and a link usage rate. With this operation, a path is effectively selected according to a network state. As described above, in the QoS routing technology, it is necessary to obtain the quality information of a path or a link.
In a network logically constructed on a base network such as an overlay network, physical nodes such as routers, switches, and the like on the base network are interposed between adjacent overlay nodes. Thus, since quality information is also changed according to a traffic state of the base network underlying the network, it is difficult to obtain accurate quality information only by a local node.
Accordingly, as disclosed also in Japanese Patent Application Laid-Open Publication No. 2006-109454, quality information is obtained by measuring the quality of a path and link. Further, since all the quality information cannot be obtained by a local node in the MPLS network described above, it is necessary to determine the quality information such as a delay, a loss ratio, and the like by measurement.
A method of obtaining the quality information of a path is roughly divided to two types, that is, an active measurement and a passive measurement. The active measurement is a method of measuring communication quality by creating a measurement-dedicated flow separately in addition to a user flow and flowing the measurement-dedicated flow to a to-be-measured path or link. The passive measurement measures quality by observing a user's flow without using a special measurement flow. Further, as one of advanced methods of the passive measurement, there is a method called an inline measurement. The inline measurement measures communication quality by comparing the transmission interval of a packet with the reception interval thereof while adjusting a packet interval of a user's flow.
However, the methods of obtaining quality information by the measurement described above have the following problems.
A first problem resides in that when the active measurement is used as a measurement method, a measurement flow applies an extra load to a network. To measure quality of a path and link, a measurement packet must be periodically transmitted to a network, which causes a measurement traffic to apply a predetermined load to the network. More particularly, when the transmission bandwidth of a path is narrow or when the measurement packet is sent to a jammed path and link, a larger load is applied thereto. As a result, the transmission of an ordinary packet fails.
A second problem resides in that when the passive measurement is used as the measurement method, there is a possibility that measurement accuracy is lowered. In the passive measurement, since a user's traffic is used to measurement, when a sufficient user's traffic does not exist, it is difficult to obtain a significant value as measurement data.
Accordingly, an object of the present invention is to provide a technology for improving measurement accuracy while suppressing the overhead of a measurement traffic in an apparatus for carrying out QoS routing based on a result of measurement of the quality information of a path or link.